Oldspot said:
First thing is that volt meter says 44.5
35598265-EEFA-4148-850F-DEB35E18629F.jpeg
When measuring what specific points?
If you can also take off the other side panel opposite the one you have so far, it should expose the tabs on the other end of the cells, and possibly the BMS as well (if it's inside that enclosure with the cells).
Then you can measure voltage of each cell (or group) with the meter probes, one meter lead at each end of each cell that you can see. I would make a list starting at the most negative cell first, which is the cell group with the fat wire (probably black) going to the BMS board. Measuring every cell you will probably have 40 voltages (see below), each pair of which will probably be identical, but potentially differetn (if there is a balance problem) between each pair.
It's not completely clear how they have the cells grouped/connected together, but I would guess they are 2p; it looks like 20 cells in each stack, and 40 cells in 2p would give a 20s2p pack. Each black block (foam?) probably covers the interconnect of four cells--two positive terminals in parallel connected to two negative terminals in parallel, with a balance / sense wire to the BMS from each of these connnections.
The group ends should then be shifted at the other end of the box so they overlap the points that on this side are between the black blocks.
If that's the case, you should get the same voltage across each cell in each pair, measured across the ends of the cells.
After you have measured at the cells themselves, then if you can also access the BMS's connector plug where the balance/sense wires go, try to measure each pair of pins, starting at the most negative end, at the actual solder joints on the BMS board itself. That will test if the wires are connected and working correctly, all the way from cells to BMS. If they are, all the voltags should be identical to the ones read off the cells themselves.
Some notes below:
Right so still couldn’t see much
FD9C1DCE-7D02-4EBC-8DFC-26B803CABC2C.jpeg
Wow. Pardon my phrasing, but that's pretty crappy for a company-built battery.
(wouldn't be bad for a home-built pack, but that's not what it is)
About a third of that volume is torn up foam (?) padding, not cells. Another large amount is just air. I doubt even half the volume of the pack is cells.
Thanks, the package was 62kg
480x310x290 so big lump
Ok, so I looked up the cell size for my 2kwh pack, and it calculates out to be
237x137x252mm
which gives a volume of 8182188mm cubed
I'm going to guesstimate that you have maybe 300mm at most of that 480mm being cells, and maybe 250mm of the 310mm being cels, and maybe 250mm of the 290mm being cells, making the actual pack size something like
300x250x250mm
which gives a volume of 18750000mm cubed, which is only 2.3x that of my pack's cells. If they are similar Wh per volume cells, then that is about 2.3 x 2kwh = 4.6kwh. (less than half of the claimed 10kwh).
If there are 40 cells, then to be a 72v 150Ah pack, at 20s 2p, each cell would have to be a 75Ah cell. Size-wise, that seems unlikely.
If this is true, then the cells probably also can't supply the current the pack is rated for, aside from the capacity, so they probably sag in voltage significantly under higher loads, and may trigger the BMS shutoff at those times.
Further, the cells would be being used harder (probably a lot harder) than they are designed to be, so they are aging faster and becoming even less capable.
It would be harder and harder for the BMS to rebalance the pack during charging, and take longer and longer for this to happen. When it gets really bad it could take many days just sitting on the charger to rebalance.
EDIT: found a post of mine
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1255590&hilit=scale+weigh%2A#p1255590
that states the 14s2p (28 cell) pack weighs about 35lbs, rounding up. That's about 16kg for 2kwh (it has brass busbars that are probably a couple pounds of that, but there is no outer pack casing). To get a 10kwh pack of these, I'd need 5 times that weight, or about 80kg....